A couple days ago I made an encosure for the
interface
circuit. Over the past couple days I've been working on
getting the reverse circuit to work, and today I soldered
it and built an enclosure for it. This circuit's job is to
prevent the car from being switched from drive to reverse
or from reverse to drive while the car is in motion. If the
reverse switch is switched to reverse while the car is
driving, the green drive light turns off and the red
illuminated reverse switch blinks on and off until either
it is put back in the drive position or the car comes to a
full stop. It works the same for going in drive from
reverse. The circuit can tell if the car is moving by
checking for a current accross the motor terminals. This
board has 18 components per square inch and 72% of the perf
holes are used.

There is a picture at
http://www.craterfish.org/teamprodigies?pictures?2006/Jul

I finished soldering the interface circuit today. This
circuit has 12 connection wires total. It has two power
wires, three wires for the gas pedal potentiometer, three
wires for the brake pedal potentiometer, one wire for
reverse, and three wires (direction, high-side power, and
low-side power (PWM)) to control the four H-bridge
circuits. These last three have indicator lights soldered
onto the board - a red LED for direction, a green LED
connected to the PWM signal, and a yellow LED for high-side
power. I tested the circuit on the H-bridge circuit I've
built with one of the motors and it worked great.

This is a complicated little circuit. When
generating a PWM
signal, it must ignore the gas pedal position if the brakes
are on. In addition to generating the PWM signal, this
circuit has to give the motor controller a direction
signal. This signal must be forward if the gas pedal is
down and the car is going forward and backwards if the gas
pedal is down and the car is in reverse, but in both
situations it must be inverted if the brakes are on. It
uses an XNOR gate (or snore gate as I like to call it) to
accomplish this. It also has an output to turn the high-
side MOSFETs in the H-bridge circuits on or off. They are
on whenever the brakes are off and off when the brakes are
on.

This is definitely one of my more-compact circuits.
It's
smaller than the voltage doubler circuit. With a total
component count of 56 and dimensions of 2 1/8" x 1 1/4",
there are approximately 21 components per square inch, and
that's not including wires. Of the 286 holes in the perf-
board, 211 of them have a component lead or wire through
them. That's 74% of the holes that are used. Look at the
pictures
(http://www.craterfish.org/teamprodigies?pictures?2006/Jul)
to see what I mean.

A few days ago I made a nice little enclosure for the
voltage doubler circuit. It might even be water proof!
There is a picture on July's
progress page
(http://www.craterfish.org/teamprodigies?pictures?2006/Jul).
Yesterday I
finished and printed out a circuit for all the vehicle's
core electronics. Last count I think there were 75
transistors.

I made an enclosure for the H-bridge circuit. It is sealed
except for the two ends, so that air can flow through it to
dissipate the heat. Now it's time to design the PWM
generating circuit and forward/reverse/braking control
circuit.

I posted a picture on the progress
page for June:
http://www.craterfish.org/teamprodigies?pictures?2006/Jun

I soldered the H-Bridge circuit that I designed. I noticed
a major flaw in the circuit design - I had it so that
either the left MOSFETs were both on or the right MOSFETs
were both on which would short out the circuit and melt
stuff. Fortunately I noticed this before I soldered the
circuit. The new diagram is at
http://www.craterfish.org/teamprodigies?pictures?2006/Jun,
along with pictures of the
finished motor controller. The heatsinks are set up in such
a way that the entire circuit board will go inside a tube
that will have air flowing through this. I may put a fan
in, or I may just have an air intake on the front of the
vehicle.

The motor controller is user-proof. It has two wires for
the motor, a ground wire, +12V, +24V, a direction input,
high control, and low control. The high and low control
wires turn the power on or off to the high-side and low-
side MOSFETs. The low-side power can be controlled with
PWM. The high-side MOSFETs would be turned off for
regenerative breaking, while the low-side remained on with
PWM.

I soldered the voltage doubler circuit today. When I was
designing the component layout I spaced everything out as
far as I could stand. Normally I try to make everything as
compact as physically possible, but usually the circuit
stops working and I throw it away because I don't know what
went wrong and there's no way to find out. This way
hopefully nothing will go wrong in the first place, as it's
very organized and well-made, and if something does, I will
be able to test at points and fix a bad connection or
whatever it is.

Go to June's progress
page
(http://www.craterfish.org/teamprodigies?pictures?2006/Jun)
to see a picture of the soldered circuit-board!

So it turns out the voltage doubler circuit wasn't perfect
either. When the multivibrator capacitors were small
(0.1MFD) for some reason it made the output stage
transistors overheat. If the 47MFD capacitors were removed,
they did not overheat. I imagine the problem was caused by
some sort of voltage spike from the capacitor, but it only
mattered at high frequencies. This may be a problem with
the new circuit also. Another problem with the old circuit
was that the output voltage was actually about three volts
less than twice the input voltage. I haven't tested this
circuit, but the new output stage should get the voltage
within a fraction of a volt of twice the input voltage.

Notice the difference in the output stages between the two
circuits - I switched the position of the NPN transistor
and PNP transistor. The old version was fail-safe; it was
impossible for both transistors to be on at once. With this
system, however, I had to choose four resistors to create a
voltage divider that would ensure that only one of the
transistors was on at once. If the input voltage is above
15V, the voltage divider no longer does this, and both
transistors will turn on which will short negative to
positive and melt the transistors. The benefit of this
output stage is the much larger range in voltage.

Go to
http://www.craterfish.org/teamprodigies/?pictures?2006/Jun
to see the new voltage doubler circuit!

I did some tests on the H-bridge circuit and made several
modifications. One change was to switch the NPN power
driving transistors with PNP transistors which saved a
couple volts. Another change was to replace the diodes from
the direction input with NPN transistors. It turned out the
voltage drop accross the diodes was too much to pull the
bases of the transistors low. I also made the smallest
amount of resistance from negative to positive in the logic
part 10 kiliohms rather than 1 kiliohm to save power, which
is important when using the +24V source. It's also nice to
save power wherever possible on an electric vehicle,
because those miliamps add up!

Go to
http://www.craterfish.org/teamprodigies/?pictures?2006/Jun
to see a schematic diagram of the new H-
Bridge circuit!

I did some research on the internet and discovered the
solution to a high-power charge pump - the push/pull
driver. This is just a combination of a PNP transistor and
an NPN transistor, but it allows the output of a circuit to
be shorted high or low with no resistors in between, which
is what I needed. I designed and built a new circuit, and
it passed my tests. I posted a circuit schematic at
http://www.craterfish.org/teamprodigies/?pictures?2006/Jun.

I redesigned the H-Bridge circuit. The new design is much
simpler, and hopefully won't melt any more MOSFETs. I put a
circuit schematic on the progress page at
http://www.craterfish.org/teamprodigies/?pictures?2006/Jun.
Since that voltage doubler circuit melted too, I'll have to
redesign that.. and I'm realizing that the new design will
have to be capable of powering a load that draws more
current than just MOSFETs - in the H-Bridge circuit I
designed the 24V source has to power some of the logic
circuitry also. I also realized that the current draw of
the last circuit was limited by a 1k resistor, so at 24V
that would be a max of 24 mA. There was also a voltage drop
accross the 1k resistor whenever the circuit was powering a
load, which caused some problems.